Global Navigation Satellite System (GNSS/GPS)
- Anthony Luo
How it works
In general, “GPS” or “GNSS” refers to a category of devices which are able to receive multiple satellite signals in order to accurately calculate the devices geographical position. There are three segments to a “GPS” system:
The space segment contains of multiple satellites which constantly emit signals. Receivers in the user segment constantly listen for these signals and are able to determine where they are in relation to the satellites! The control segment is largely used to ensure that satellites remain where they should be, and that they continue to work and function as intended.
On some GPS devices, there will also be a compass built in so that the GPS can determine the heading (or direction) that it is pointed in. Other GPS will use two (or more) receivers to determine heading from the difference in GPS locations.
What do we use it for?
GNSS Systems are able to offer in the range of centimeter to meter level accuracy. We use GPS to aid in position hold, ensuring that the drone remains in one “area” of space! We also commonly use GPS for navigation (waypoints are all GPS pairs), where knowing our position accurately allows us to fly towards a different known point in space.
Warg commonly uses a few different GPS sensors, all with different accuracies & Capabilities:
Name / Link | Compass (y/n) | Accuracy | Extra Features |
|---|---|---|---|
TBS NEO m8 | n | ~2.5m |
|
Sparkfun NEO M8 | both | ~2.5m |
|
y | ~1.5m | Safety Switch | |
Vectornav VN-300 | y | ~0.6m | Internal AHRS |
Constrains & Mounting Requirements
GPS modules with compass may need to be mounted in a specific orientation. Please ensure that you follow manufacturer guidelines when mounting such devices.
Different modules will also come in different shapes & have different mounting patterns. Please refer to manufacturer datasheets for different devices.
Here are some common mounting constraints:
Flat, pointed straight up | GPS Receivers are ceramic patches, and should be mounted so they are parallel to the ground and pointed up as often as possible. |
|---|---|
Unobstructed view of the sky | GPS Signals can easily be blocked by carbon fiber, metal, or wires. It’s important that GPS antennas have clear view of the sky. |
Away from electrical interference | the less noise you have on your receiver, the better the signal and the better the accuracy. |
In general, it can be beneficial to mount the GPS close to the center of the drone when you are using one gps. However, if you are using multiple GPS, it is beneficial to space them out as far apart as possible, so as to reduce the area of convergence and improve overall system accuracy. Remember to add offsets for the GPS when you do this!